Multi-spectral and hyper-spectral sensors have been used for a variety of purposes. For example, these types of sensors may be used in a number of object recognition and detection applications for mapping, weather monitoring, precision agriculture, urban planning, and security systems, among other applications.
Multi-spectral and hyper-spectral sensors measure radiation emitted by a given surface or object as well as radiation reflected from the surface or object in a number of different narrow spectral bands. By obtaining images of the given surface or object in a number of different narrow spectral bands, various characteristics of the surface or object can be determined and/or discriminated, such as temperature, color, composition, etc.
Some multi-spectral sensors use multi-quantum-well (MQW) sensor arrays with a number of sensing regions whose sensor elements can be composed of layers of semiconductor material. The sensing regions can sense radiation in particular wavelength bands.
While having the ability to obtain image information of surfaces in multiple wavelength bands simultaneously, many multi-spectral and/or hyper-spectral sensors can be expensive to manufacture and/or have a larger size than is suitable for some applications.
Quantum mechanics are also utilized in other fields of technology. For example, quantum dots, also referred to as semiconductor nanocrystals, are materials whose size is on the order of the exciton Bohr radius of the material such that the electron energy levels can be treated as discrete, rather than continuous. The size of the band gap of these materials can be controlled by adjusting the size of the dot (e.g., by adding or subtracting atoms).
The ability to control the size of the band gap also allows for the ability to “tune” the absorption and/or fluorescence characteristics of each quantum dot. For example, quantum dots have tunable absorption onsets and emission patterns. That is, increasing or decreasing the size of a quantum dot and/or altering the type of quantum dot material can change the peak emission wavelength and/or the wavelength of the first exciton peak associated with a particular quantum dot.
Some examples of quantum dot materials include lead-selenide, lead-sulfide, lead-telluride, cadmium-selenide, and cadmium-sulfide, among others. These materials can be provided in various forms including thin films, resins, powders, or as particles, among other forms.
The ability to tune absorptive and fluorescence characteristics of quantum dot materials makes them useful in a number of filtering applications. For example, quantum dot thin film materials may be used as wavelength filters in waveguide structures of optical devices (e.g., in fiber optic media, etc.).
One example includes the use of quantum dots as a saturable absorber material in an add/drop filter within a fiber optic communication system. In this example, the quantum dot thin film material, sandwiched between two planar mirrors, allows for a specific wavelength within a particular wavelength band to be transmitted.